Relative risk of lung cancer in relation to number of cigarettes smoked2

Relative risk

No of cigarettes smoked per day:

0

1

1-14

8.1

15-24

12.7

>=25

25.1

The risk of developing cancer is reduced by stopping smoking and decreases substantially after five years. Even in those who have smoked for many years, life expectancy is increased when smoking stops. After 10 or more years of not smoking an ex-smoker has nearly the same risk as a non-smoker.